Shostak's new book Confessions of an Alien Hunter makes a strong case for continuing SETI as our digital capabilities expand. Indeed, given the daunting challenge of interstellar distances, it could be argued that our sole contact with extraterrestrial civilizations, if they exist, will take place through communications from afar, mediated by radio or light.

Let's face it, the numbers are tough. The fact is that we can already do interstellar travel, provided we're content with transit times of many tens of thousands of years, which is what our fastest spacecraft ever, New Horizons, would take to reach Proxima Centauri. A quick look at alternatives leads Shostak to note that ion engines aren't up to the challenge, while antimatter requires the creation and storage of vast amounts of exotic, hard to contain particles. Wormholes? Fine, but we don't know yet whether they exist or how to use them.

If all this sounds depressing, consider Shostak's alternative, the use of telepresence to extend human vision, hearing and touch to our stellar neighbors. Thus we go, but we go robotically, sending what he calls "proxy explorers" to nearby stars, aided by ever increasing miniaturization that allows us to make payloads tiny. Perhaps the idea is a driver for nuclear-powered rocket technologies whose development has stalled:

A plausible solution would be to re-energize NASA's development of nuclear-powered rockets, with the intention of building a craft able to send clusters of micro-bots into deep space at velocities of, say, one-tenth light speed. Depending on financing and our ability to garner international cooperation, these probes could be sent off before the 21st century starts to wane. By the middle of the following century, on-the-scene data from Epsilon Eridani, the nearest known planetary system, could be in our hands.

Virtual wanderings through a data feed from another star are compelling indeed, fueled by our telepresence proxies and data collectors. Who wouldn't want to plug into the Epsilon Eridani Channel, immersing the senses in a wrap-around virtual experience that not only allows us to explore another planetary system, but also suggests that the wave of such exploration is ever outward?

Here I want to plug in another quote from the book, which is a lively and satisfying account of what it's like to be SETI's major spokesman in today's world. Here Seth is talking about various schemes for interstellar travel and he touches upon new physics:

Numerous and highly intriguing schemes have been proposed to do this. Alas, most of them require marshaling massive amounts of energy or rounding up exotic material that might not even exist. Scientists will not say that such schemes are impossible. We also can't say whether they are possible, because theories in this field are still incomplete. Yet even if one of these schemes eventually looks right on the blackboard, there is no guarantee that it is feasible in practice.

Exactly so. The key statement is "theories in this field are still incomplete." Completing them is not the work of a single lifetime, nor is the resultant coupling of theory with technology that may develop. As we examine realistic technologies like telepresence via robotic probes, what can be done to keep our investigations of other possibilities alive?

For as lively as telepresence would be, many of us would like to go one better. Propulsion research is a parallel stream, one that continues to flow even as we tune up and deploy the latest technologies available to us. Pushing its limits may or may not result in breakthroughs of the sort Shostak mentions. But one thing we can say for sure is that if we stop searching for them because of our current limits, we won't find them.

And if they're not there to be found? Here's the point: By focusing our efforts on the nature of the possible, we should learn more about how the universe works, which is an end in and of itself. I've been asked on more than one occasion what will happen if scientists fail to find a way to achieve the kind of travel we see in Star Trek. The answer is that we'll take different, slower methods to get to the stars, but we will still have learned a great deal about physics along the way, identifying key issues and sketching in many unknowns.

That's a quest worth taking. And while it's reassuring to realize that the kind of telepresence probes Shostak is talking about are feasible in a not terribly distant future, we still find ourselves confronted with a universe whose vast mysteries - dark energy, dark matter, the very nature of gravity - point to possibilities we have yet to explore. Nature yields up her secrets but slowly and often confronts us with surprises, which is why we must keep basic research alive. And if we create an Epsilon Eridani or Tau Ceti Channel along the way, count me an avid subscriber.